1. Field of the Invention
This invention relates to a catalytic process for mild hydrocracking of heavy oils. More particularly, this invention relates to a mild hydrocracking process for the hydrodemetallation (HDM), hydrodesulfurization (HDS) and hydroconversion (HC) of a heavy hydrocarbon feedstock boiling above 650.degree. F., such as vacuum gas oil (VGO) and VGO containing a high proportion of vacuum resid (VR) to lighter distillate products boiling at or below 650.degree. F.
In the mild hydrocracking process of this invention a sulfur- and metal-containing hydrocarbon feedstock, such as residua containing heavy oils, is contacted at an elevated temperature with hydrogen and a catalyst composition comprising a specified amount of a Group VIII metal, such as an oxide of nickel or cobalt, a specified amount of an oxide of molybdenum and, optionally, a specified amount of an oxide of phosphorus, such as phosphorus pentoxide supported on a porous alumina support containing a dealuminated Y-zeolite. In the catalytic mild hydrocracking process of this invention the sulfur- and metal-containing hydrocarbon feed is contacted with hydrogen and the catalyst containing dealuminated Y-zeolite, which has a specified pore size distribution, in a manner such that an increased production of middle distillates and a substantially higher conversion of the 1000.degree. F.+ fraction of the hydrocarbon feed to the 1000.degree. F.- lighter products is achieved over that obtained with the use of prior art hydroprocessing catalysts while high levels of sediment formation are avoided.
2. Prior Art
U.S. Pat. No. 4,600,498 (Ward) teaches a process for mild hydrocracking a hydrocarbon oil having a substantial proportion of components boiling below about 100.degree. F. which comprises contacting the hydrocarbon oil under conditions of elevated temperature and a hydrogen pressure less than about 1500 psig with a particulate catalyst comprising at least one hydrogenation component, a Y-zeolite having a unit cell size between about 24.40 and 24.64 .ANG. and a dispersion of silica-alumina in a matrix consisting essentially of alumina.
U.S. Pat. No. 4,894,142 (Steigleder) discloses a highly selective hydrocracking process providing increased yields of middle distillates. The process employs a catalyst comprising a hydrogen form Y-type zeolite having a unit cell size between about 24.20 Angstroms and 24.40 Angstroms, a metal hydrogenation component and refractory oxide support materials. The catalyst is characterized by low ammonia temperature programmed desorption (TPD) acidity strength which may be achieved by dehydroxylation caused by a dry calcination.
U.S. Pat. No. 4,430,200 (Shihabi) discloses hydrocarbon conversion catalysts having reduced aging rates and exhibiting lower gas yield in conversion processes made by pre-steaming a large pore, high silica zeolite such as mordenite or zeolite Y and base-exchanging the steamed zeolite with an alkali metal to reduce the acidity to a low value.
U.S. Pat. No. 4,654,454 (Barri, et al.) discloses a process for converting C.sub.2 to C.sub.5 hydrocarbons to aromatic hydrocarbons which comprises bringing the hydrocarbon into contact with a surface dealuminated zeolite loaded with a gallium compound.
U.S. Pat. No. 4,533,533 (Dewing, et al.) discloses a process for selective and controlled dealumination of an alumino silicate zeolite by heating a zeolite having pores filled with coke in air at a temperature of 450.degree. F.-650.degree. F. The partially dealuminated zeolite is useful in toluene disproportionate processes.
U.S. Pat. No. 5,069,890 (Dai, et al.) discloses novel treated zeolite, such as Y-zeolite, prepared by treating charge zeolite, such as a dealuminated Y-zeolite (which is essentially free of Secondary Pores), with steam for 5-60 hours at 1000.degree. F.-1500.degree. F. Product is particularly characterized by increased Secondary Pore Volume (pores of diameter of 100 .ANG.-600 .ANG.) in amount of as high as 0.20 cc/g and is useful in resid hydroprocessing.
U.S. patent application Ser. No. 07/533,222, filed Jun. 4, 1990 of Dai, et al., now U.S. Pat. No. 5,112,473, discloses a process for preparing acidified dealuminated Y-zeolites prepared, for example, by treating a dealuminated Y-zeolite with an acidic medium, such as an aqueous solution of an inorganic acid.
U.S. Pat. No. 5,053,374 (Absil, et al.) discloses low acidity refractory oxide-bound zeolite catalysts, for example, silica-bound ultrastable Y-zeolite, possessing physical properties, e.g., crush strength similar to those of their alumina-bound counterparts, and since low acidity refractory oxide-bound catalysts are inherently less active than alumina-bound zeolite catalysts, the former are particularly useful in hydrocarbon conversion processes in which reduced coke make increased catalyst cycle length. Due to their stability in acid environments, the low acidity refractory oxide-bound zeolite extrudate can be acid treated without unduly comprising structural integrity.
U.S. Pat. No. 4,919,787 (Chester, et al.) discloses an improved method for passivating metals in a hydrocarbon feedstock during catalytic cracking which involves contacting the feedstock with a passivating agent comprising a precipitated porous rare earth oxide, alumina, and aluminum phosphate precipitate. The passivating agent may be coated on a cracking catalyst, such as dealuminated Y-zeolite. Y-zeolite, etc., be part of the matrix of a cracking catalyst, or be added to the cracking operations as discrete particles.
U.S. Pat. No. 5,037,531 (Bundens, et al.) discloses a catalytic cracking process using a catalyst comprising a framework dealuminated Y-zeolite which is rare earth and aluminum exchanged.